1. Field of the Invention
The present invention relates to a heat sink for cooling LSI packages having various structures used to cool electronic apparatuses typically represented by computer systems, a method of manufacturing the same and an LSI package to which the heat sink is mounted, and more specifically, to a structure of a heat sink having fins attached to a heat diffusion plate and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, LSI chips have a heat generating density ranging from about several watts/cm.sup.2 to about several tens of watts/cm.sup.2 and thus an LSI package including LSI chips packed therein can be cooled by supplying air flow thereto or a simple arrangement in which a flat plate with a good heat radiating property is disposed on the backside of the LSI package. Recently, however, as an amount of heat generated by LSI chips is increased, heat sink structures excellent in cooling performance are needed.
Among them, a pin-fin shaped heat sink structure may be contemplated as a preferable structure when both the advantageous mounting and the improvement of heat radiating performance are taken into consideration. As disclosed in Japanese Unexamined Patent Publication No. Hei 3-250652, there is a heat sink composed of thin wires whose diameter is selected so that the Reynolds number thereof is 40 or less, as an example using the above structure.
The LSI package cooling heat sink is composed of thin wire fins made by bending a continuous long metal (Cu) wire and joining the same to a heat diffusion plate.
Further, there is another heat sink arranged such that thin wire fins joined to be wide wire-shaped members or support columns spaced apart from each other at predetermined intervals are processed to a corrugate shape and then joined to a heat diffusion plate through metal, and the like to improve the rigidity of the heat sink.
In these prior art LSI package cooling heat sinks, when the thin wires fins are processed to a corrugate shape or while they are handled, these wires fins are irregularly located or not formed to a uniform shape due to the low rigidity of the thin wire fins regardless of that the wide wire-shaped members or support columns are provided at predetermined intervals to improve the rigidity of the heat sink. As a result, the respective heat sinks or products are apt to have a varying performance and thus are less reliable.
Further, the thin wire fins must be carefully bent to the corrugate shape because the thin wires are less rigid. Therefore, a long time is needed to bend the thin wire fins to the corrugate shape.
Further, when the thin wire fins are joined to the heat diffusion plate, a joining surface is deformed due to the lack of rigidity of the thin wire fins. As a result, the thin wire fins do not come into intimate contact with the heat diffusion plate and are not joined well thereto, and thus a problem arises in that a cooling performance is lowered.
Further, a problem also arises in that a discharged cooling wind has a pressure lower than that of a changed cooling wind (hereinafter, referred to as a pressure loss) due to the existence of the wide wire-shaped members or support columns provided with the thin wire fins to improve the rigidity thereof and thus a cooing effect is lowered. That is, the design of the heat sink does not take the flow and cooling performance of a cooling wind into consideration.
Further, since the thin wire fins are formed to a uniform shape, the temperature of the thin wire portion located just above a heat generating portion (LSI chip) is greatly increased as compared with that of the other thin wire portion and thus the thin wires of the former portion may be oxidized, which causes a problem from a view point of reliability in a long term. Moreover, in this LSI package cooling heat sink, the heat diffusion plate is irregularly heated and a heat resistance is increased.